Sound recording, monitoring system



April 18, 1950 L. T. SACHTLEBEN SOUND RECORDING, MONITORING SYSTEM 2 Sheets-Sheet 1 Filed April 18, 1947 (Iitorneg I April 8, 1950 L. T. SACHTLEBEN 2,504,590 I SOUND RECORDING, MONITORING SYSTEM Filed April 18, 1947 2 Sheets-Sheet 2 82 d8 F 014, L /w% l v 20 7007, I

Mr/m/ @ttorneg Patented Apr. 18, 1950 UNITED SOUND RECQRDING, MONITORING SYSTEM Lawrence T. Sachtleben, Haddonfield, N. J., as

signor to Radio Corporation of America, a corporation of Delaware Application April 18, 1947, Serial No. 742,360

13 Claims. 1

This invention relates to sound recording equipment and particularly to the optics of a monitoring system for a sound on film recorder.

Monitoring systems for sound on film recorders whereby the amplitude of vibrations of the modulating element and the excursion of a noise reduction element are visibly indicated are well known. Also, monitoring systems for visually indicating the condition and position of the recording light source have been used. For instance, monitoring systems of this general type are shown in my U. S. Patent No. 2,423,256 of July 1, 1947, and in copending Dimmick application Ser. No. 629,295, filed November 17, 1945, now U. S. Patent No. 2,468,048, granted April 26, 1949. Although these prior systems provide indications of the adjustment of the modulating and noise reduction elements, the present invention has several advantages over the prior arrangements.

In the present system the monitoring images are projected upon the rear of a translucent screen and viewed from the front of the screen. The images are formed by light projected normal to the screen while the screen is tilted substantially 30 from the vertical. This feature of the monitoring system permits an observer of average height to view the images in line with the projection thereof which provides maximum brightness of the images when the screen surface is only partially diffusing, such as, for example, the surface of finely ground glass. Another feature of the monitoring system is that it permits the light source monitoring optics to be made integral with the lamp socket and at lamp filament height Without producing keystone effects in the screen image. This permits maximum protection for the monitoring optics and provides a good general appearance of the whole optical system.

The monitoring optics for indicating modulation are all substantially in a vertical plane which permits their being mounted as an integral subassembly instead of isolated elements which may get out of alignment with respect to each other. The present invention is directed to the optics of the monitoring system, the mechanical arrange-v ment of the various groups of elements being disclosed and claimed in my copending application Ser. No. 743,620, filed April 24, 1947.

The principal object of the invention, therefore, is to facilitate the monitorin of a sound recording system.

Another object of the invention is to provide an improved method of and system for visually indicating the action of a sound recording modulating element.

A further object of the invention is to provide an improved optical path for visually indicating the movement of a light beam.

A still further object of the invention is to provide an improved optical system for observing the image of a moving light beam and a station'- ary light source.

A still further object of the invention is to provide an improved optical path in association with the path of a recording light beam for indicating the modulation of the light beam and the condition of the source providing the light beam.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation will be better understood by referring to the following description read in conjunction with the accompanying drawings forming a part hereof, in which:

Fig. 1 is a diagrammatic perspective view of the monitoring optical system of the invention shown in association with the recording optical system;

Fig. 2 is a view showing the type of apertures which may be monitored with the invention;

Fig. 3 shows another type of aperture which may be monitored with the present invention;

Fig. 4 is a superimposed view of the light beam images, the slit, and a shutter type noise reduction element; and

Figs. 5 and 6 show two types of monitoring images received on the monitoring screen.

Referrin now to Fig. 1, a light source in the form of a lamp 5 provides light for the recording system. The light from the lamp 5 is collected by lenses ii and projected to an aperture plate 1, which is of the type shown in the upper section of Fig. 2, and which will produce a class A pushpull type of sound record. This aperture plate is provided with two sound track apertures l6 and a vertical rectangular monitoring aperture ll. Emergent light from the apertures l0 and I! is reflected at right angles by a prism I2 and then projected by a lens l3 to a mirror I4 of the usual modulating galvanometer. From the mirror M the light passes through a slit condenser lens Hi to a slit mask H, the sound recording light beam passing through a horizontal narrow slit 2!]; through a dichroic monitorin reflector 2|, and an objective lens 22 to a film 23. This general type of sound recording optical system is disclosed and claimed in my copending application Ser. No.

514,225, filed December 14, 1943, now U. S. Patent No. 2,436,671, granted February 24, 1948, one type of monitoring system therefor being disclosed and claimed in my above mentioned copending application.

The sound record light beam has been indicated by the broken line 25 while the monitoring light beam passing through the aperture ll has been indicated by the broken line 26. The monitoring light beam through the aperture ii passes through the same optical elements as the record ing light beam between thelight source and the slit plate 91 at which point it passes through a vertical rectangular monitoring window 28.

The image of the aperture ll in mask 1 is caused to fall in the plane of the slit plate I? by the prism l2, lens l3, and lens id. The light of the recording beam passing to the film 23 forms an image of the mirror 84 in the objective lens 22 through the action of condenser lens it. The light through the-aperture ll, vibrates in accordance with the recording light beam to the film 23 since :both are modulated by mirror lsgthe monitoring beam, however, being intercepted by a lens 38 which is cemented to .a prism 3| positioned behind the window 28. This light, as

shown by ray 25, is incident upon lens '30 at a point-near its edge which'is closest to the main optical axis shown by ray 25. The optical center of *lens 3- 3 is somewhat farther removed from the main optical axis 25 so that the lens 39 exhibits :a prismatic action rendering the axis or principal ray of the monitoring beam parallel to the main optical axis 25 upon refraction at the first surface of lens 3!], so that this-ray remains in a vertical plane parallel to the main optical axis 25 until it is reflected to the monitoring screen.

After refraction by lens 30, the monitoring light isrefiected downwardly by prism 3| to a spherical lens 33. The curvature of the first surface of lens 3-0 is such that a stationary image of mirror It is formed in lens 33, whose power is suchtha't an image of the plane of window 28 is finally formed on the monitoring screen 37 at a magnification of approximately five times. Lens 33 is adjustable axially for focus.

From lens 33 the monitoring light passes to an isosceles trapezoidal prism 35 which carries the light to the rear toward the mirror i i and then directs it vertically to a front surfaced plane mirrored positioned behind ..-a translucent vrear projection screen 31 to which the monitoring light is reflected. The screen 31 is :tilted about its lower edge to .make an acute angle of about 30 with the vertical such that the light from the mirror .gfistrikes the screen! perpendicularly to form image 38. This arrangement of the screen 3! permits theimage 38 to be viewed coincident with the line :of projection of light from the mirror fit. As screen 3] is positioned about 4:8 inches 1 above the floor-when attached to the recorder, the average observers line of sight will coincide with the line of projection to provide maximum brightness of the image 38. Also, keystoning of the image 38will be avoided since the projection axis is not tilted with respect to the surface of the screen.

In addition to monitoring the mirror vibrations the condition of the filament of the lamp 5 is also indicated on the screen 31. The optical system for the light source includes a reflector 46 which reflects light in a horizontal plane to a spherical lens ll behind which is an aperture plate '42. The light is then reflected downwardly by mirror it to a mirror which projects the light at an angle of approximately 30 to the horizontal to the screen 31 as shown by image 41. Thus, the beam of light from mirror 45 strikes the screen 37 at right angles and the image 47 suffers no keystone effect and is parallel with the line of light from the mirror 38 to the screen 38. As the image 47 may be viewed coincident with the axis of the light beam producing it, maximum brightness is provided. The magnification of the filament is substantially 3.75 times.

To provide a light meter for the modulating beam, an optical unit comprising a spherical lens 50 and reflecting prism 5| cemented together may be inserted in the beam of light whenever it is desired to read its intensity. The elements 50 ands! are mounted so they do not normally intercept the beam 25 and are inserted into the beam whenever a reading is desired. They have, therefore, been shown in dotted lines. The intercepted light beam is projected downwardly by prism .Cal through a pair of plates 52, one of which may be a filter, to a photo-'voltaic cell 53, to which may be connected any suitable type of meter. .A meter system of this general type is disclosed and claimed in Collins U. S. Patent No. 2,233,914 of March 4, 1941.

For the purpose of monitoring the signal being recorded, a dichroic reflector 2| positioned in the light beam reflects the red end of the spectrum upwardly through a pair-of cylindrical lenses 5'! .to a double reflecting prism 58. The light from the prism 58 passes through a'plane glass plate 68,2. cylindrical lens 5! ,theaperture of a plate 62, .a pair of splitting cylindricallenses 63, plane glass plate iii to .a push pull photoelectric cell 55. The lenses 5? image the 'slitonxthe lenses 63. The cell may beconnected to a pair of head-phones or a loudspeaker for monitoring the light variation as impressed on the film :23. A monitoring system of this basic type using a dichroic reflector is disclosed and'claimed in Dimmick U. S. Patent No. 2,314,39210-f March 23, 1943.

As an illustration of a practical monitoring system for the visual observation of the degree of modulation and the condition of the. light source,

the distance from the plate 11 .to the reflecting surface of the prism 3| was A05 inch, while the distance from the prism '31 to the reflecting surface of the trapezoidal prism was 1.625 inches.

v, The light was reflected rearwardly a distance of positioned 1.375 inches from the filament of lamp 5, while :the reflector 44 is positioned 2.272 inches from themirror .40, the lower mirror 45 being .426 inch below mirror 44, The distance of projection from mirror 45 to screen 31 was 7.773 inches. For purposes of comparison, the vertical distancefro'm reflector 2i to prism 58 was 1.688inches while the distance from reflector 58to photo-cell was 2.032 inches. In the light meter unit, the distance fromthe reflecting surface of prism 5! to the light cell53 was 2.5 inches.

As mentioned above, any of the four masks shown in Figs. 2'an'd 3 at 'i', 51, 68 and-69, may be used in the system of Fig. l, mask 7 producing a class A push-pull track, mask "61 producing a single duplex track, mask 68 producing-a class B push-pull track, and mask 69 producing either a negative or a positive double bilateral track. The slit plate ll may be used with either of the masks 7, 67 or 58, while the slit plate 10 may be used withthe mask-'69 as disclosed and claimed incopending Dimmick application Ser. No. 629,- 294, filed November 17, 1945, now U. S. Patent No. 2,468,048, granted April 26, 1949. Furthermore, masks I and 61 use shutters to obtain noise reduction, class B mask 68 requires no noise reduction and mask 69 uses a biased galvanometer.

Selecting mask 1 to illustrate the monitoring image 38 in the system, reference in made to.

Figs. 4 and 5 wherein the cross hatched areas H and I2 represents the light image from apertures ID on the slit plate I! and slit 20. The cross hatched area 13 represents the light image passing aperture H of the mask 1 and projected through window 28. The edge of the noise reduction shutter vane is shown by broken lines 15 in which is an opening 16, the vane also having a tab H which intercepts light between the window 28 and the lens 30 in accordance with the position of the vane 15. The opening 18 is located close to the slit 29 and between it and the lens 39 where it moves up and down in accordance with the amplitude of the rectified signal currents. Thus, the light reaching the film 23 depends upon the position of the images "H and 12 with respect to slit 29 and the position of the openings 16 with respect to the slit 29. The images II and 12 vibrate normal to the slit 29 in accordance with the instantaneous variations of the signal currents while theopening it moves perpendicular to the slit in accordance with the. envelope of the signal currents. At time of no signal the respective position of the images H and i2 and the opening 15 is as shown on the drawing, there being two narrow bias lines a and b of light passing to the film 23.

The light image 13 will be projected through the above described system to the screen 31 and will appear as a horizontal rectangle of light shown in Fig. 5 by the cross hatched portion. That is, the point 89 corresponds to the end 8| of the beam 13 while the po nt 82 corresponds to the point 83 where the tab 11 intercepts the beam 13. Now, when the images H and 12 are modulated, that is, vibrated normal to the slit, the end 89 will likewise vibrate and spread until the end 89 appears at point 85 at 100 percent modulation which is the time when the sloping sides of the beams H and 12 reach the ends of the slit 29. Should the beam be 209 percent over modulated the end of the beam will then extend to the point 88.

As the amplitude of the signal increases the opening it is moved downwardly which moves the tab 7? downwardly, thus, shortening the left hand end of the beam as seen in Fig. 5. The system is adjusted so that the sloping edges of the opening 16 will contact the ends of the slit 29 when the amplitude of the signal is 80 percent of full modulation and this corresponds to a shortening of the left hand end of the beam to a point such as shown at 88. Further downward movement of opening '16 will not uncover any more of the slit 29 but may be indicated by further shortening of the beam to point 89. The point 88 may be represented by point 90 on the image 13. Thus, the position and the amplitude of vibration of the modulating light beam will always be shown by the horizontal image 38, and, because of the optical path and the position of the image, it will have maximum brightness.

As mentioned above the aperture 69 uses the biased galvanometer. That is, instead of the rectified signal currents being employed on the shutter 18, it is impressed on a second winding of the galvanometer and varies the average position of the mirror I4 When this s stem is usedthe image at 38 appears, as shown on the shaded portion of Fig. 6, between points 9| and 92, this image being formed by light passing through either aperture 93, or 94, according to whether the upper or lower edge of the aperture is being employed. If apertures 93 and 94 are oil-set horizontally their images will appear off-set vertically as disclosed and claimed in the above mentioned co-pending Dimmick application. To indicate the amplitude of modulation this shaded area vibrates according to the amplitude of the signal and end .92 will move to point 99 for 100 percent modulation and to point 91 for 200 percent modulation. The amount of noise reduction is indicatedv by the position of the image 9l92. During modulation the beam 9l--92 moves to the right and vibrates about mean posi-- tions to the right, the amount of this displacement of the means position being indicated by the distance marked bias deflection.

I claim:

l. A sound recording monitoring system com prising a light source, and an aperture plate illu" minated by said light source and having a sound recording aperture and an adjacent, verticallyelongated, rectangular monitoring aperture therea in, means for vibrating in a vertical plane the: light passing through the recording aperture and through said monitoring aperture, a slit plate having therein a recording slit and a vertical 1y elongated, rectangular monitoring window through which the monitoring light passes, a first. optical element for downwardly reflecting said monitoring light passing through said window, a light beam modulator between said monitoring window and said first optical element, a second optical element for directing said monitoring light from said first optical element parallel to the path of said light from said vibrating means to said slit plate in said vertical plane, said sec ond optical element also directing said light upwardly in said plane, an observation medium, and means for deflecting said vertically directed light perpendicular to said observation medium.

2. A sound recording monitoring system in accordance with claim 1, in which optical means are provided for reflecting light directly from said light source in a horizontal plane, in a downward direction, and perpendicular to' said observation medium.

3. A sound recording optical system comprising a light source, an aperture plate having a recording aperture and an adjacent elongated monitoring aperture therein, a slit plate in a substantially vertical plane having a horizontally elongated, rectangular recording slit therein, and a vertically elongated, rectangular monitoring window, means between said aperture plate and said slit mask for vibrating the light passing optical means for deflecting said vibrating light passing through said monitoring window and modulated by said modulator in a vertical plane to the rear of said observation medium, and

means for reflecting said light perpendicular to said observation medium.

4. A sound recording optical system in accordance with claim 3 in which optical means are provided for projecting light directly from said light a ing a:lightsourcawarm-aperture -plate having; .a

light passing reqording aperture-and a vertically elongated, rectangular flight: passing monitoring aperture, therein,.a.slitplateghaving a horizontal- 1y elongated, rectangular light passing recording :slit and a verticaHyfikmgated,rectangular light passing monitoring; window, .a screen. mounted above said slit plateuand l tiltedattan tanglev to: the

vertical and anioptical system-adapted to de fleet a ;light-; image; of; said, monitoring aperture in: a -plural-ityoi-edirectionsrin; a wertical plane, to magnify I said; lighti image ,;and 1toaproject, said .s. ima e $11 endicularlyto the.-rearrsurface of; said screen.

8. A sound recording optical systemzinaccordanceu'with :clai-m 7 in which; an; element is :provided. behind and adjacent saidwindow-ior vary. ing the; length, of th imase f: said o t in aperture in. accordancc iwith the average amplitu gid-variation of the-signal beingarecordedig 9.v Asound recording. optical t systemqin-;accord- Y ance with: claimes 15in ;p, which optical ;means, are

provided forrefl,ecting=;light"from saidzlight-source detected in the same'plane in. which-the light :ls projected through; said recording and monitoring apertures of said--- aperture v:plate, said; optical means projecting an ima e LOf-E said -lightr source perpendicularly-towthe rear, surface iofczsaid screen iii; A soundg-recording optical vsy-stemzin: accordiance with claim ,,9 :-in': whi'ch= means are provided for intercepting ,;a mortiumpfi; t fi h ripa i w-a said recording slit forz-detecting the wariationsin STU? thal ehtzpass nersai filitn 1'1 A sound recording monitcrmgsystemecm prising a -light "source, an aperture plate having an- -aperture for 1 passingua recording' light beamand a vertically elongated-, rectangular aperture' I plate havin'g a horizontally elongated, rectangular slitl tl'ierein-'to -pass portions' of said a recording 4 light 'beam depending upon' 'the instantaneous l values- 0f: a signal being irecordediand'a verticallyr for passing a monitoring light-beam;said wams being 1 in a substantial horizontal plane, -a slit elongated} rectangular windoWtherein: to pass said monitoring lightbea'm, one. end of said beam 1 varyingzin accordance with the -tinstantaneous" VaIUGSF Of said signal, a screen above saidifslit Y platekand tilted atan. angle" to a vertical plane; opticalwmeans forrprojectingr an I image of said monitoringiaperturein.ai'vertical plane and per:

pendicular to. said J screamiand lm'eans adjacent saidii'slit platezifor varying the other endiofi: said-" ,monitoring beam in "accordance with the varia-" tions in amplitude of said signal;

12. Afsound recording system inaaccordance with: claim 11 inwhich' optical means are '-'provided-for'projectingan image of said light'source' normal=to:said screen, said meansin'cluding a 1 magnifying lens and apluralityof' reflectors for detecting .light' rays from-said source ina plane coincident with'the lightrays through said apertunes;

beam; LAWRENCE TISACHTLEBEN.

REFERENQES CITED The following references are of record-in the file? of this patent UNITED STATES PATENTS 13 A sound recording; systems-in accordance with claim '11 mwhich means :are'irprovided for" determining the intensity Of'TSZid recording:light 1 "Number si ne Date 2,166,185 Stack 1 .July: 18,':1939' 2,166,186 Stack July 18,- 1939 2,220,198 Batsel 1 Nov.' 5, t 1940' I 2,270,350 Schomacker Jan. 20,1942 2,289,054 Dimmick -July '7, 1942 2,318,138 Benfer May 4,'1943- 

